Would a performance chip or an exaust leak at the manifold cause a trouble cods p0405? This isbmy second EGR valve.
Your code is a low voltage signal for EGR so check the wiring from the EGR to the ECM, so somewhere the 5 volts to or the signal voltage from the EGR is dropping too low, look for any rubbed through spots, corrosion in connectors, pay very close attention to the grounds, the computer controls need to have a good grounds, weak or missing ones can cause you all kinds of misery.
What kind of performance chip?
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